Cyclone separators in various different constructional forms are used in a number of devices and/or equipment for separating impurities contained in gaseous fluids, such as solid particles or dust, droplets of liquids or similar material.
Cyclone separators are widely used for separating and/or removing particles from the air or from process gases. They are also used as chemical reactors, heat exchangers and for drying granular materials and combustion of oil. In petroleum refineries, they are used for ensuring the continuity of the process for obtaining products, retaining a catalyst and impeding its emission into the atmosphere, preventing loss and pollution. The great applicability of cyclone separators is due to their low operating cost, easy maintenance and the possibility of withstanding severe temperature and pressure conditions.
Cyclone separators can be used in various different arrangements, in series or in parallel. In some processes, all of the gaseous fluid produced, which shall hereinafter be called gas-solid suspension, passes through the separator. In other processes, cyclone separators can be used as part of the waste gas cleaning system.
The particles are separated by a process of centrifugation of the gas-solid suspension. This phenomenon occurs with the induction of a vortical flow inside the cyclone separator due to the significant tangential force component with which the suspension enters the cyclone chamber, which is generally of a conical shape. Being of greater density than the gases, the solid particles have a greater tendency to remain in the trajectory perpendicular to the vortical flow, due to centrifugal force and thus to collide with the walls of the chamber. With the collisions, the particles lose speed and tend to separate from the flow, falling towards the bottom of the chamber, from where they are removed. The gas separated goes out through the outlet pipe of the cyclone, after moving in several revolutions through the chamber and in a curve with an accentuated angle towards the pipe in the upper part.
Cyclone separators of gas-solid suspensions are generally of the reverse flow type, which are the most conventional ones for this type of separation. However, unidirectional flow cyclones are also used, principally in applications where the concentration of solids in the suspension is low.
In reverse flow cyclones, the gas outlet pipe, usually called the finder or vortex pipe, is fixed and located in the upper part of the cyclone. During operation, there is a need for the total reversal of the vortical flow of the gas so that it is sucked by the outlet pipe.
In unidirectional flow cyclones, also known by the English term “uniflow”, the gas outlet pipe is located in the lower part of the cyclone, there consequently not being a need for reversal of the vortical flow.
In these two configurations, the cyclone separator comprises only one separation zone, the unidirectional flow separator having a separation zone length shorter than that of a separator with reverse flow, this being the reason why the unidirectional flow separator is efficient only in gas-solid suspensions with low concentrations of solids.
Although the separation zone of the reverse flow separator is larger, the flow reversal zone is the region in which the greatest loss of collection efficiency of the cyclone separator occurs.
The instability existing at the flow reversal apex results in lateral displacements of the vortical flow, causing entrainment of solids previously separated and erosion of the cyclone separator walls.
U.S. Pat. No. 4,238,210 discloses a unidirectional cyclone separator which comprises an internal duct, which forms a flow path, with a central body provided with vortical flow generating helixes extended externally. The duct is enclosed by a collecting chamber and the helixes have collecting ends and channels which open through the wall of the duct to the inside of the collecting chamber. Downstream from the vortical flow generating helixes, there are outlet slots which are transverse with respect to the gas flow.
As with the other unidirectional cyclone separators, this equipment is efficient only for suspensions with low concentrations of solids.
The device and method described below are an alternative which has advantages for the separation of gas-solid suspensions with respect to the devices and methods known in the prior art for low and high concentrations.